Hexafluorodimethylcarbinol terminated alkane- and alkenethiols

ABSTRACT

A hexafluorodimethylcarbinol terminated compound, method of making it, and a composition of matter are disclosed. The compound may have the formula (CF 3 ) 2 C(OH)-L-M-R. The substructure L may be selected from an optionally substituted propenylene group (—CH 2 CH═CH—) and trimethylene group (—CH 2 CH 2 CH 2 —). The substructure M may be selected from a substituted or unsubstituted methylene chain, a substituted or unsubstituted oxyalkylene chain, and a silicon-containing chain or combination thereof. In one embodiment, M may be selected from —(CH 2 ) n —, —(OCH 2 CH 2 ) m —, and —(Si(CH 3 ) 2 O) p —Si(CH 3 ) 2 — (CH 2 ) q —, wherein n is at least 1, e.g., n is up to 10, m can be at least 1, e.g., m is up to 10, p can be 0 and in one embodiment is from 1 to 10, and wherein q can be 1 and in one embodiment is from 1 to 12. The substructure R represents one of a halogen, —SH, —SZ, —S—S-M-L-C(CF 3 ) 2 (OH), wherein Z represents a thiol protecting group.

This application is a divisional application of allowed U.S. patentapplication Ser. No. 14/138,686, filed on Dec. 23, 2013, which is adivisional application of U.S. Pat. No. 8,618,330, issued on Dec. 31,2013.

BACKGROUND

The present disclosure is generally related to ahexafluorodimethylcarbinol terminated thiol compound, to a precursor forforming the compound, to a general synthetic procedure for forming thecompound, and to a sensor device which incorporates the compound.

Fluoroalcohol and thiol functional groups confer unique properties onmolecular substances, which qualify them for many applications. Theunique properties associated with incorporation of the fluoroalcoholfunctional group include strong hydrogen bonding interaction and protonacidity coupled with a hydrophobic character. This combination ofproperties makes fluoroalcohol substituted compounds surface activeagents in aqueous systems and, as such, they find applications assurfactants, wetting and dispersing agents, defoamers, phase transferagents, and polymer blend formation promoters, etc. For detection of theorganophosphorus chemical warfare agents, the hydrogen bondedinteraction of the fluoroalcohol alcohol with the phosphoryl group isadvantageous for the sensitivity and selectivity of point sensors inthis application. The thiol functional group is beneficial for itscoordination with metal ions and for its coordination with neutralmetals. As such, the covalently bonded adsorption of thiolfunctionalized molecules to metal surfaces has been extensively used asa metal surface treatment, and it has found many applications thatinclude nano- and molecular electronics, soft lithography, contactprinting, nano-particulate composites, chemical sensing, corrosionresistance, adhesion promotion, and electrochemistry. Numerousw-functionalized n-alkenethiol compounds have been synthesized andinvestigated for properties and applications involving metal surfaces.

One particular application is in chemical species detection, which hasled to developments of sensor assemblies that include a film ofcore-ligand material. U.S. Pat. Nos. 6,221,673 and 7,347,974, to Snow,et al., disclose one such chemical sensor assembly, wherein metal ormetal alloy nanoparticles are encapsulated by a monomolecular layer ofligand molecules. The ligand molecule has a chain structure with a thiolfunctional group at one end and a heteroatom functional group at theother end. The thiol group bonds to a metal atom of the nanoparticlesurface, and this heteroatom functional group interacts with vapors inthe environment. In these disclosures, the heteroatom functional groupis a hexafluorodimethylcarbinol structure.

A trifluoromethylcarbinol terminated thiol is disclosed in U.S. Pat. No.7,189,867 ('867), to Wynne, et al. This compound was designed from thesame considerations dating back to use of the hexafluorodimethylcarbinolin polymer coatings for sensor applications described in Snow et al, J.Appl. Poly Sci. 43, 1659 (1991). The '867 patent discloses a molecularagent for monomolecular coatings on metal and metal oxide surfaces. Thecompound is of general formula CF₃—CH(OH) —CH₂-(L)_(n)-CH₂—SH, wherein Lcan be a substituted or unsubstituted methylene, a substituted orunsubstituted oxyalkylene, or an alkyl-substituted or unsubstitutedsiloxanylene. The '867 disclosure includes a synthetic procedure forforming the compound.

BRIEF DESCRIPTION

A first exemplary embodiment of the disclosure is directed toward acompound represented by the formula (CF₃)₂C(OH)-L-M-R. In the compound,L is selected from an optionally substituted trimethylene group(—CH₂CH₂CH₂—) and an optionally substituted propenylene group(—CH₂CH═CH—). M is selected from substituted or unsubstituted methylene,substituted or unsubstituted oxyethylene, and a siloxane chain, andcombinations and multiples thereof. R is selected from a halogen, —SH,—SZ, and —S—S-M-L-C(CF₃)₂(OH). Z represents a thiol protecting group.

A second exemplary embodiment of the disclosure is directed toward acomposition of matter including a metal surface having a group of thegeneral formula (CF₃)₂C(OH)-L-M-S— bonded thereto, in which L and M aresubstructures as defined above.

Another embodiment of the disclosure relates to a method of forming ahexafluorodimethylcarbinol terminated thiol compound, which includes (1)reacting a ω-halo-α-olefin with hexafluoroacetone to form a firstintermediate; (2) optionally hydrogenating a double bond of the firstintermediate to form a second intermediate; and (3) transforming thefirst or second intermediate by first reacting it with thiourea followedby base hydrolysis to form the compound.

Another exemplary embodiment of the disclosure is directed toward anencapsulated particle comprising a hexafluorodimethylcarbinol terminatedthiol compound. Such particle finds use as a vapor responsive electronictransducer in a chemical sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is flow chart showing a method of producing ahexafluorodimethylcarbinol terminated thiol compound according to oneembodiment of the present disclosure;

FIG. 2 is a flow chart showing a method of forming the exemplarycompound and detecting an organophosphorus compound with the exemplarycompound;

FIGS. 3A-3B illustrate a method preparing ligand encapsulatednanoparticles including the present compound by direct synthesis;

FIGS. 4A-4B illustrate a method of preparing ligand encapsulatednanoparticles including the present compound by exchange synthesis;

FIG. 5 is a perspective view of a sensor comprising a film ofnanoparticles encapsulated by the exemplary hexafluorodimethylcarbinolterminated thiol compound;

FIG. 6 shows a magnified representation of the hydrogen-bondedinteraction between the hexafluorodimethylcarbinol moiety of a clusterligand shell and a phosphonate ester vapor in a sensor configuration;

FIG. 7 is a graph showing a response of a sensor exposed to purge (DMMPoff) and exposure (DMMP on) cycles of a phosphonate ester vapordelivered by a vapor generator, where the signal strength (arbitraryunits) roughly corresponds to measured current; and,

FIG. 8 is a graph showing the maximum magnitude response for a sensorvs. DMMP vapor concentration for a sensor based on a stabilized goldnanocluster comprising the hexafluorodimethylcarbinol terminated thiolcompound in accordance with another exemplary embodiment of the presentdisclosure.

DETAILED DESCRIPTION

One aspect of the present disclosure is directed toward ahexafluorodimethylcarbinol terminated compound (“the compound”). In oneembodiment, the compound includes a hexafluorodimethylcarbinolfunctionality and a thiol functionality (or a precursor therefore),which are connected by a chain. A chain, as used herein, is a series of(at least three) linked atoms, wherein the hexafluorodimethylcarbinolmoiety and the thiol group are linked to different atoms that are bothpart of the same chain. The present disclosure is also directed toward acompound having specific application in coatings for chemiresistorsensors. In some aspects, the compound includes functionalities of thetypes that either bond to the metal nanoparticles surface of a sensor orinteract with targeted chemical vapors to be detected.

The disclosure is directed to compounds having ahexafluorodimethylcarbinol functional group at a first end of amolecular chain and a thiol group (or a precursor for the thiol group)at a second end. The molecular chain can be a substituted orunsubstituted hydrocarbon chain, which can be saturated or unsaturated,a substituted or unsubstituted oxyalkylene chain, an alkyl-substitutedor unsubstituted silicon-containing chain, or a combination thereof. Themolecular chain can be of variable length. However, in one embodimentthe molecular chain is up to 18 carbon atoms in length (or, where thechain includes heteroatoms selected from Si and O, no greater than 18atoms in length). For some applications, such as certain sensorapplications, the molecular chain may be no greater than 13 carbons orlinked atoms in length. In some cases, a resistance of a coating formedof compounds of longer chains may be too high. Longer chains (i.e.,thicker shells) tend to correlate with too low conductivity. (See, U.S.Pat. No. 6,221,673 (“'673”) and U.S. Pat. No. 7,347,974 (“'974”), toSnow, et al., the disclosures of which are incorporated herein in theirentirety by reference; see also, “Metal-Insulator-Metal Ensemble GoldNanocluster Vapor Sensors”, in Defense Applications of Nanomaterials,Miziolek, et al., Eds., American Chemical Society Symposium Ser. No.891, Washington, 2004, Ch. 3). In one embodiment, the chain has no fewerthan three carbons. Chains of shorter lengths tend not to stabilize asefficiently. Sensors coated with compounds having shorter length chains(i.e., thinner shells) tend to short electrically. For example, thinspots in a monolayer of the compound can cause adjacent metalnanoparticles of the sensor to contact and fuse thereby bypassing themonolayer's modulation of electrical resistance and shorting the sensor.These thinner shells also tend to correlate with instability towardagglomeration.

As used herein, a silicon-containing chain is an optionally substitutedchain comprising at least one silicon atom which is spaced from theterminal thiol group or thiol precursor by at least one carbon atom, thesilicon-containing chain being free of Si to Si bonds. Such a chain isexemplified by substituted and unsubstituted siloxanes and silanes,which are alkyl terminated, at the thiol end of the molecule. In oneembodiment, the silicon-containing chain is linked to the thiol or thiolprecursor by an alkyl group of up to 5 carbons in length.

As used herein a thiol precursor includes a group which can react ordecompose to form a thiol or sulfur terminated ligand.

As used herein, “substituted” means that at least one hydrogen connectedwith the molecular chain is substituted with a substituent, such as analkyl, alkenyl, alkoxy, halo or hydroxyl group, or combination thereof,which substituent may be shorter, in length than the molecular chain,e.g., from 1-6 carbons in length.

The following exemplary carbon-containing chains can be situated betweenthe thiol group and the hexafluorodimethylcarbinol group: a linear alkylgroup; a branched alkyl group; a saturated alkyl group; an unsaturatedalkyl group; a branched cyclic alkane; a branched cyclic alkene; asubstituted chain; an unsubstituted chain; and, a combination thereof.In one embodiment, the carbon containing chain can contain one or moreheteroatoms, such as, Si and/or O, and may include, for example, analkyl-substituted or unsubstituted chain which includes silicon, asubstituted or unsubstituted oxyalkylene, and combinations thereof.

The compound may have a general structure which can be represented asfollows: (CF₃)₂C(OH)-L-M-R. The substructure L may be selected from apropenylene group (—CH₂CH═CH—), a trimethylene group (—CH₂CH₂CH₂—),which can be substituted or unsubstituted, and combinations thereof. Thesubstructure M may be selected from a substituted or unsubstitutedmethylene chain, a substituted or unsubstituted oxyalkylene chain, andan alkyl-substituted or unsubstituted silicon-containing chain, andcombinations and multiples thereof. In one embodiment, M may be selectedfrom —(CH₂)_(n)—, —(OCH₂CH₂)_(m)—, and—(Si(CH₃)₂O)_(p)—Si(CH₃)₂—(CH₂)_(q)—, and combinations thereof. Thesubstructure R may represent a thiol group or a precursor thereof, whichis capable of being converted to a thiol group by reaction orsubstitution. R can be selected from a halogen, —SH, —SZ, and—S—S-M-L-C(CF₃)₂(OH), wherein Z represents a thiol protecting group. Inparticular, the compound can be derivatized as the disulfide or with awell-known thiol protecting group, in which case Z can be selected from—COCH₃, —COCF₃, —COC(C₆H₅)₃, —C(CH₃)₃, —C(C₆H₅)₃, —CH(C₆H₅)₂, and—CH₂(C₆H₅). n, m, and p may each assume integer values of at least 0,providing that the chain represented by —C-L-M- is at least three atomsin length, and in one embodiment wherein the L moiety is at least 3atoms in length.

In one embodiment, n is at least 1. In one embodiment, n is up to 16,and in another embodiment, up to 10. In one embodiment, n is up to 5. Inone embodiment, n is 1 or 2. In one embodiment, m is at least 1. In oneembodiment, m is up to 10. In one embodiment, m is up to 4. In oneembodiment, m is 1. In one embodiment, p is at least 1. In oneembodiment, p is up to 10. In another embodiment, p is up to 5. In oneembodiment, p is 1. In one embodiment, q is at least 1. In oneembodiment, q is up to 12. In one embodiment, q is 1-3. In anotherembodiment, q is at least 3. In one embodiment, q is 1. In oneembodiment, q is 3.

In one exemplary embodiment, the compound is of the structure(CF₃)₂C(OH) —CH₂CH₂CH₂—(CH₂)_(n)—SH, where n is as described above. Inanother embodiment, the compound is of the structure (CF₃)₂C(OH)—CH₂CH═CH—(CH₂)_(n)—SH, where n is as described above. In anotherembodiment, M is —(OCH₂CH₂)_(m)—, where m is at least 1. In anotherembodiment, M is —(Si(CH₃)₂O)_(p)—Si(CH₃)₂—(CH₂)_(q)—, where p is atleast 0 and q is at least 1. In one embodiment, q is at least 3. In oneembodiment, q is 3. In one embodiment, R is —SH. In another embodiment,R is bromine.

FIG. 1 shows a general synthetic procedure for forming the compound.Generally, a starting compound comprising a terminal (a) olefin andhaving the general structure CH₂═CH—CH₂-M-X is reacted withhexafluoroacetone (step a). In one embodiment, the substructure X can bea halogen. The substructure M represents a carbon-containing molecularchain as described above, comprising entirely carbon atoms or in whichone or more of the carbon atoms may be replaced by a heteroatom selectedfrom Si and O and where the carbons in the chain may be substituted orunsubstituted. The carbon-containing molecular chain can include, forexample, a substituted or unsubstituted methylene, a substituted orunsubstituted oxyalkylene, an alkyl-substituted or unsubstitutedsilicon-containing group, and combinations thereof. Some embodimentsemploy a four or five carbon chain. In one embodiment, the startingcompound has no more than 13 carbons in the main chain linking X withthe terminal C═C. The synthesis is considered general to a range ofalkane or alkene chain lengths, as well as for the substitutions ofother types of foregoing chains. The electrophilic addition of thehexafluoroacetone with the terminal olefin forms a first intermediatehaving the formula (CF₃)₂C(OH)—CH_(2—)CH═CH-M-X, wherein the double bondshifts one unit from the initial olefin end of the chain, and thehexafluorodimethylcarbinol functionality links to the terminal carbon.This first intermediate is optionally hydrogenated (step b) to form asecond (alkane) intermediate (fully saturated chain) of the formula(CF₃)₂C(OH)—CH₂—CH₂—CH₂-M-X. The substructure X of the first or second(e.g., alkane or alkene) intermediate is displaced by thiourea, and athiouronium adduct is formed (step c). The thiouronium adduct ishydrolyzed by a base (step d) to form the product compound.

As a specific example, the following exemplary synthesis illustrates theprocess using a halogen terminated terminal alkene (structure 1) as thestarting compound. The exemplary synthesis employs an alkene chainhaving five carbons. The carbon-carbon double bond is situated at theolefin end of the chain, where it can undergo electrophilic addition ofhexafluoroacetone. The halogen group is situated at the opposite end ofthe molecular chain. A bromine atom is the halogen utilized in theexemplary synthesis.

A first synthesis is described for production of ahexafluorodimethylcarbinol terminated alkenethiol (compound 4). Inparticular, the first step a of the synthesis is the electrophilicaddition of hexafluoroacetone with a ω-halo-α-olefin as the startingcompound having the formula CH₂═CH—CH₂—CH₂—CH₂—X, where X is a halogen(e.g., Br). This step a may be performed using the procedure describedin Urry, et al., J. Org. Chem. 1968, 33, 2302. In the above reaction,structure 1 (5-bromopent-1-ene) forms the adduct(CF₃)₂C(OH)—CH₂—CH═CH—CH₂—CH₂—Br, shown as structure 2. This additioncauses the double bond to shift one unit from the initial olefin end ofthe chain. The double bond in structure 2 may be cis, trans, or amixture of the two isomers. The alkylbromide is then converted to athiol (step c) by reaction with thiourea and subsequent base hydrolysis(step d). This reaction may be performed using the procedure outlined inUrquhart, et al., Org. Synth. Coll. Vol. III 1955, 363. Thioureadisplaces the bromide substituent to form a thiouronium bromide adduct(step c), which is not isolated but hydrolyzed by addition of a base(step d) to form the product of structure 4. The double bond in theresultant product is usually present as a mixture of both cis and transisomers, but may also be exclusively cis or trans.

A second synthesis is described for preparation of ahexafluorodimethylcarbinol terminated alkanethiol. This procedure is thesame as described above except that a step b is added. This secondsynthesis is described below using the foregoing 5-carbonω-bromo-α-olefin, 5-bromopent-1-ene (structure 1). The first step a ofthe synthesis is the same as the foregoing procedure resulting instructure 2: the electrophilic addition of hexafluoroacetone tostructure 1, which forms the adduct (CF₃)₂C(OH)—CH₂—CH═CH—CH₂—CH₂—Brshown as structure 2. The next step b includes hydrogenation of thebromoalkene intermediate 2 to form a corresponding bromoalkaneintermediate (CF₃)₂C(OH)—(CH₂)5—Br of structure 3. The third step c andfourth step d include conversion of the bromoalkane intermediate to thealkanethiol product of structure 5. These steps are analogous to steps cand d described above.

While the method and other methods of the disclosure are illustrated asa series of steps, it will be appreciated that the various methods ofthe disclosure are not limited by the illustrated starting materials orthe illustrated sequences of such steps. In this regard, it is to beappreciated that the synthesis can be performed utilizing any of avariety of starting materials, wherein the X sub stituent can be anyfunctionality that is capable of being replaced by a thiol group orprotected thiol group. Some steps may occur in different orders and/orconcurrently with other steps apart from those illustrated and describedherein, in accordance with the disclosure. It is further noted that notall illustrated steps may be required to form the compound of thepresent disclosure. The methods of the disclosure, moreover, may beimplemented in association with the disclosed starting materials, aswell as with other starting materials not illustrated or described,wherein all such alternatives are contemplated as falling within thescope of the disclosure and the appended claims.

In structure 4, the double bond positioned beta to thehexafluorodimethyl carbinol group is relatively unreactive due toelectronic induction and steric effects. The individual steps of thepresent disclosed syntheses (referenced above as steps “a”, “b”, “c”,and “d”) provide excellent yields; they may be conducted on multigram orlarger scales. The presence of the double bond in the alkenethiolproduct of structure 4 does not cause a significant difference inproperties between compounds 4 and 5, so the somewhat lower yield forthe hydrogenation step b of the second synthesis can be avoided byforming the alkenethiol product of structure 4 in place of thealkanethiol product of structure 5.

The electrophilic addition a of hexafluoroacetone to the terminal olefincan be performed under temperature conditions in a range between 25° C.and 210° C., depending on the olefin reactivity. Additions at highertemperatures tend to cause byproducts because the reaction occurs toofast. Additions at lower temperatures can cause the reaction to occurtoo slowly. In one embodiment, the electrophilic addition occurs at atemperature between 130° C. and 140° C.

The hydrogenation step b that converts the first (alkene) intermediate 2to the second (alkane) intermediate 3 is performed in one embodimentutilizing a palladium and/or a platinum catalyst on a carbon carrier.Other embodiments can utilize either the platinum and/or the palladiumcatalyst on other carrier materials. These catalysts can be loaded up to2%, 5% and 10% by weight of the carrier. The embodiment disclosed hereinutilized a 10% loaded carrier to achieve the hydrogenation step b.

It is more generally noted that a first step of the present synthesiscan utilize, as structure 1, any halogen-terminated alkene, wherein thehalogen is selected from fluorine, bromine, chlorine, iodine, andcombinations thereof. Bromide is utilized in one embodiment because analkene compound having a terminal bromine atom is relatively inexpensiveand it exhibits properties that provide higher yields in synthesisprocedures.

The hexafluorodimethylcarbinol terminated thiol compounds can beincorporated as a self-assembled monomolecular layer on the surfaces ofmetal nanoparticles (shown as step e in FIG. 1). By monomolecular, it ismeant that the layer has a thickness approximately equivalent to that ofthe length of a single molecule of the exemplary compound. Byself-assembled, it is meant that the compound bonds to the metal surfaceby way of the sulfur atom with the hexafluorodimethylcarbinolfunctionality oriented outermost in the layer. By nanoparticle, it ismeant a particle which is less than 1000 nanometers in maximum diameter,and generally less than 100 nanometers in maximum diameter. Thenanoparticle may be generally spherical in shape or have another shape,such as an ovoid, rod, plate, spike, or the like, or it can be attachedto other particles. The nanoparticle generally includes metal atoms, themetal atoms being present at the surface of the nanoparticle core orforming the entire nanoparticle. In one embodiment, the nanoparticle isformed in major part, e.g., at least 90% by weight, of metal. The metalmay include an electrically conductive metal, such as gold. As will beappreciated, while in some embodiments, the exemplary compound mayprovide 100% by weight of the layer surrounding the nanoparticle, it isalso contemplated that the compound may be mixed with other selfassembling compounds to form the layer, in which case, the exemplarycompound may comprise at least 50 mol. % of the layer.

In the exemplary embodiment, the sulfur atom of the compound covalentlyor otherwise binds to metal atoms of the nanoparticle surface, and thethiol hydrogen may be given off or it may remain associated with thesulfur atom of the compound. As used herein, an S— group bound to ametal surface is defined as including both a presence and an absence ofthe thiol hydrogen. If the compound is a disulfide, the disulfide bondis broken and each sulfur is individually bonded to the metal.

The hexafluorodimethylcarbinol terminated thiol compounds can beincorporated as a self-assembled monomolecular layer on the surfaces ofmetal nanoparticles. Assemblies of such treated metal nanoparticles arereferred to herein as ligand-stabilized metal nanoclusters. The thiolmonomolecular layer may be referred to as a ligand shell and the metalnanoparticle as a core. The '673 and '974 patents disclose suitableconductive metals which may be utilized in the present nanoparticles,such disclosures of which are incorporated herein by reference in theirentireties. In one embodiment, the metal core includes gold, due to itsstability toward surface oxidation. A film composed of an assembly ofthese ligand-stabilized metal nanoparticles (“nanoclusters”) can be usedas a transducer for chemical sensing. Sensors comprising the exemplaryligand-stabilized metal nanoparticles can be formed according to themethods disclosed, for example in Wohltjen, et al., Anal. Chem. 1998,70, 2856 and in the '673 patent.

For example, nanoparticles of gold or other metals or alloys of 0.8-40nm in maximum dimension can be encased in a ligand shell comprised ofthe exemplary compound (5) of, for example, about 0.4-10 nm inthickness. The magnitude of electron transport through such a film ofencapsulated gold nanoclusters can be dependent on the dimensions of thegold core and on the thickness of the monolayer shell (Terrill, et al.,J. Am. Chem. Soc. 1995, 117, 12537; Snow, et al., Chem. Mater. 1998, 10,947). The thickness of the encapsulating monomolecular layer includingthe exemplary hexafluorodimethylcarbinol terminated thiol compoundaround a nanometer-sized gold nanoparticle or cluster can be sufficientto allow a small amount of current to pass through adjacent clusters,while at the same time being highly modulated by the fluoroalcoholinduced adsorption of a chemical analyte.

Two exemplary methods for preparation of hexafluorodimethylcarbinolterminated thiol ligand stabilized gold nanoclusters will now bedescribed, as follows: (1) a direct synthesis; and, (2) an exchangesynthesis. These methods are shown in FIGS. 2-4.

The direct synthesis method consists of dissolving a salt of theconductive metal (or salts of the conductive metal in embodimentsutilizing alloys) of which the core is to be composed and an organicsubstance corresponding to the desired ligand in a common solvent (stepS110). In one embodiment, a gold salt is utilized, which may include,but which is not limited to, HAuCl₄. The gold salt, the organic ligandand a reducing agent, such as NaBH₄ are dissolved in a common mediumunder conditions of rapid mixing (step S120) (this step may be performedas described in M. Brust et al., J. Chem. Soc., Chem. Comm. 1994, 801).In one embodiment, step S110 further employs a phase transfer reagent,such as, for example, tetraoctylammonium bromide. As depicted in FIG. 3using, as the exemplary compound,4-mercapto-2-butenyl-hexafluorodimethylcarbinol(HSCH2CH═CHCH2C(CF3)₂(OH) (similar to the compound of structure 4,above; a synthesis for production of which is described in Example 7),the gold ions of the salt are reduced to neutral atoms and subsequentlynucleate to form multiatom cores (step S130, FIG. 2). These cores growby adsorption of additional metal atoms. Competitively, the thiol ligandmolecule is adsorbed onto the growing gold core surface (step S140),eventually encapsulating the gold core and terminating its growth. Therelative stoichiometry of gold salt to organic thiol ligand determinethe relative rates of gold core growth and thiol-ligand encapsulation,and thus the size of the core in the ligand-stabilized cluster. Thethickness of the ligand shell is determined by the size of thethiol-ligand. Examples of this method of synthesis are given below asExample 7 and Example 8.

The exchange synthesis method consists of co-dissolving an alkanethiolstabilized cluster and a free hexafluorodimethylcarbinol terminatedthiol for the ligand in a common solvent (step S150), during which anexchange reaction occurs whereby the free hexafluorodimethylcarbinolterminated thiol displaces the gold surface bound alkanethiol ligand andan equilibrium distribution of the two thiols in the free and goldsurface bound state is approached. The free thiols are then separated,and a second exchange step may follow with the addition of more of thefree hexafluorodimethylcarbinol terminated thiol (step S160). A newexchange equilibrium is approached where the displacement of thealkanethiol by the free hexafluorodimethylcarbinol terminated thiolligand is more advanced. Additional exchange cycles can be conducted(step S170) so that the ligand shell composition of the clusterapproaches 100% of the hexafluorodimethylcarbinol terminated thiolligand. This exchange synthesis method is depicted in FIG. 4, andexamples are given below as Example 9 and Example 10.

For ligand-stabilized gold nanoclusters with polar ligands that make thenanocluster soluble in polar organic solvents such as alcohols, esters,ketones and polar halocarbons, the exchange synthesis method can beutilized over the direct synthesis method. The nanocluster solubilitymakes separation of phase transfer agents (used in the direct synthesisapproach) from the cluster product difficult. This separation canrequire chromatography, which limits the scale of the reaction to smallamounts, reduces the yield of purified product, and adds to the cost.The exchange method, while generally requiring additional steps, takesadvantage of a very facile and highly scalable preparation of aprecursor cluster (alkanethiol stabilized gold clusters) by the directsynthesis method, and it avoids use of the phase transfer agent and itsattendant purification difficulties. This exchange synthesis method alsois a facile preparation route to nanoclusters with varying amounts ofdifferent ligands in the nanocluster shell, as described in Example 11and Example 12.

The encapsulated metal nanoparticles thus formed may be used as a vaporresponsive electronic transducer in a chemical sensor. Embodiments ofthis disclosure can include a sensor having a metal surface comprised ofgold, although other metals such as silver, platinum, palladium, oralloys thereof may be used. These ligand-stabilized gold nanoclustermaterials can become a component in a chemical sensor when thesematerials, comprising at least 0.1% by weight of the microencapsulatedparticles, are deposited as a continuous thin film onto a surfaceequipped with a pair of electrical contacts (step S180). The pair ofelectrical contacts can be used to detect electrical properties andchanges in electrical properties of the coating that is positioned inthe gap between the electrodes. When target molecules adsorb and desorbinto and out of the nanocluster film, the accompanying electricalproperty change is transduced into an electronic signal by this sensingdevice. A very useful configuration for such electrical contacts on asurface is the interdigitated electrode, shown in FIG. 5, and describedin further detail below, which may be fabricated on an insulatingsubstrate as described in U.S. Pat. No. 6,221,673. This configuration ofelectrical contacts has a very large cross-sectional area to gap ratio,and the electrodes themselves are very closely spaced (ranging from 0.01to 1000 micrometer and, in one embodiment, from 1 to 100 micrometer) andthin (ranging from 0.1 to 10 micrometer and, in one embodiment, from0.50 to 5 micrometer). As also described in U.S. Pat. No. 6,221,673,there are several ways for depositing S180 the thin film of nanoclustermaterials onto the surface of an electrode device, which includespraying from solution as a fine mist, casting a film on the surface byevaporation of solvent from a deposited solution of clusters, andchemical self-assembly using coupling agents which bond individualclusters to the surface and to each other. Typical thicknesses of thedeposited cluster film range from 0.005 to 10 micrometers. Oncedeposited, the film of clusters is characterized by a baselineelectrical property in an inert environment. Such a property is anymeasurable response to application of an electrical field and includes aresistance, impedance, capacitance, etc. Typically, the resistance ofthe device ranges from 0.001 to 100 MΩ and in one embodiment in a rangeof 0.01 to 1 MΩ.

The sensor thus fabricated is then exposed to an environment (step S190)in which a concentration of a targeted chemical species resides. Thechemical species may be present in the environment as a gas, vapor,aerosol, or liquid. When the sensor is exposed to the environment S190containing phosphonate esters or other organophosphorus chemical warfareagents, the hexafluorodimethylcarbinol groups at the outer surface ofthe ligand stabilized nanoparticles interact with the phosphorylsubstructure of the warfare agents in the environment (step S200). Theinteraction S200 can be detected by a change in the electrical property,such as the conductivity, of the sensor.

One chemical species which may be targeted by the sensor is thephosphonate ester class of compound, and the molecular interaction isone of a strong hydrogen bond donor (the hexafluorodimethylcarbinolmoiety in the ligand shell of the cluster) interacting with a stronghydrogen bond acceptor (the phosphoryl functional group of a phosphonateester compound) to form a hydrogen-bonded complex. FIG. 6 presents adepiction of this hydrogen-bonded interaction from a sensor perspective.In this depiction, there is a partitioning of the phosphonate esterbetween the vapor phase and that adsorbed by way of hydrogen bondingonto the ligand shell of the assembly of clusters forming the coating onthe interdigital electrode sensing device. The adsorbed phosphonateester perturbs the response of the ensemble of nanoclusters in the filmto an electric field by way of changing the distances betweenneighboring metal nanoparticle cores and by altering the permittivity ofthe medium between these cores as well. The simplest electrical propertyto measure is the passage of current through the assembly of clusters inthe gaps between the electrodes.

The relative resistance change of a sensor responding to phosphonateester vapor exposure and purge cycles is shown in FIG. 7. A vaporexposure and purge cycle entails the alternate delivery of a stream ofair with a known concentration of vapor for a fixed duration of timefollowed by a stream of pure air to purge the sensor housing for a fixedduration of time. The “on” part of the cycle refers to the vaporexposure, and the “off” part of the cycle refers to the pure air purgepart of the cycle. The sensor device is coated with a film of4-mercapto-2-butenyl-hexafluorodimethylcarbinol ligand-stabilized goldnanoclusters. The phosphonate ester is dimethylmethylphosphonate((CH₃O)₂CH₃PO) (DMMP). DMMP is a frequently used physical simulant forphosphonate ester-based chemical warfare agents. The responses to thisvapor are rapid and reversible. FIG. 8 shows the linear dependence ofthe same sensor response to varied concentrations of DMMP (in ppm). Theslope of this line or simply a point within its range characterizes thesensitivity of the sensor. The detection limit extends to ppb andsub-ppb concentrations and is dependent on measurement electronics used.

Referring once more to FIG. 5, the exemplary sensor system 10 includes asubstrate 22, which is formed of an electrically insulated material,such as quartz. A pair of interdigitated, electrically connectedelectrodes 24, 26, having comb-like configurations, is deposited on thesubstrate 22. The electrodes 24, 26 may be formed of gold fabricated onthe quartz substrate 22. A thin film 27 composed of a multiplicity ofligand-stabilized nanoparticles formed using the exemplary compound isdeposited on the interdigital electrodes 24, 26 and on the substratesurface between and in contact with the electrodes 24, 26. This thinfilm is an ensemble of closely packed nanoparticles having a core-shellstructure sometimes referred to as a MIME (metal-insulator-metalensemble) film. The cores are composed of an electrically conductingmetal, in one embodiment, gold, and have a maximum diameter of less than100 nm, and in one embodiment, less than 10 nm. The ligand shell iscomposed of an insulating material, but it has a thickness of amonomolecular layer. The thickness dimension of a monomolecular layerranges from 0.3 to 2 nm, and at such dimensions electron transport mayoccur by way of tunneling currents through the insulator. The adsorptionand desorption of analyte molecules to such thin insulating layers causelarge changes in the tunneling current and the electric fieldpermittivity between the metal cores. This MIME thin film is composed ofa series of many metal-insulator-metal junctions and is deposited on thesubstrate 22 to connect the two electrodes 24, 26. A circuit 28, whichincludes electrodes 24, 26, including a voltage or power source 30(e.g., a battery) and a current meter 32, or other electrical propertymeasuring device, is used to measure an electrical property, such asconductivity. The sensor device 10 is exposed to an environment 34 (seeFIG. 6) containing chemicals to be measured (e.g., gas, liquid, orsolid). A reference device (not shown) may also be provided. Thereference device is covered with a passivating layer (e.g., plastic,glass, paraffin wax, etc.), or in some other way is isolated from theenvironment, which possibly contains the chemical species of interest.The reference device provides a means to compensate for the normalchange in resistance with temperature exhibited by the MIME in thin filmapplications.

The exemplary compounds disclosed herein are capable of being utilizedin a variety of other applications. The adjacent fluorine and alcoholgroups and the thiol functional group can confer unique properties onmolecular substances. The compound may be present in a composition atfrom about 0.1 to about 100 mol %. For some applications, particularlythe sensor coatings discussed above, the compound may be present at theupper end of the range. The compound can be present at lower levels forsome applications, for example, from about 0.1 to about 5 mol % forother exemplary applications, including anti-corrosion coatings;surfactants, wetting and dispersing agents, defoamers, phase transferagents, polymer blend formation promoters, and the like.

The hexafluorodimethylcarbinol group provides enhanced properties overthe trifluoromethylcarbinol group in existing compounds. Theseproperties include stronger hydrogen bonding, more proton acidity, andgreater hydrophobicity. This combination of enhanced properties makesthese compounds improved surface active agents in aqueous systems.Furthermore, the hexafluorodimethylcarbinol portion of the compoundimproves sensitivity and selectivity of a point sensor for detection ofthe organophosphorus chemical warfare (e.g., nerve) agents, such asSarin (GB), Soman (GD), and VX. When the present compound-coated sensoris exposed to an environment having phosphonate ester vapors (shown asstep f in FIG. 1), the phosphoryl ester group of the warfare agent canbond to two available hydrogen atoms of two adjacenttrifluoromethylcarbinol groups.

The hexafluorodimethylcarbinol functionality of the compound can impartseveral advantages to the metal surfaces of which it is applied. First,the adjacent trifluoromethyl groups inductively promote hydroxyl acidityto both enhance hydrogen bonding and to sterically deter intramolecularbonding; and, (2) the fluorine presence makes the monolayer coatinghydrophobic, which reduces the coating's sensitivity to water and,hence, discourages water-induced corrosion of the metal surface.

The thiol is capable of bonding interaction with metal atoms on a coresurface of a nanocluster. Unlike existing compounds, the exemplarycompound provides alkanethiol and alkenethiol compounds that include thehexafluorodimethylcarbinol group at one end of a chain and a thiol atthe other. The hexafluorodimethylcarbinol terminated thiols are thususeful in applications for surface treatment of metals.

The exemplary embodiment discloses a novel synthetic route for forming acompound having both a hexafluorodimethylcarbinol and a thiol functionalgroup. It further provides a novel compound having adjacenttrifluoromethyl groups situated at a first end of a molecularcarbon-containing chain and the thiol group situated at an opposite,second end of the chain.

A first advantage to various aspects of the present compound is that itmay be produced at high yields as the synthesis is readily accomplished.

A second advantage to various aspects of the present compound is thathaving two trifluoromethyl groups in the hexafluorodimethylcarbinolfunctionality can enhance the unique properties associated withincorporation of a fluoroalcohol functional group. For example, thecoating can be more hydrophobic in character; hence, it can improvesensor selectivity by mitigating the effects of moisture and humidity.In particular, the additional fluorine atoms of the adjacenttrifluoromethyl groups can improve the hydrophobicity of the coatingsfor MIME sensors, as compared to a single trifluoromethyl groupavailable in existing coatings. The disclosed compound can also provideless interference from water vapor in sensing applications.

The adjacent trifluoromethyl groups may provide another advantage ofgreater sensitivity to ester molecules in phosphonate ester vapors. Inparticular, an improved hydrogen bond interaction between thefluoroalcohol groups and a phosphoryl group present in organophosphoruschemical warfare agents is achieved, thereby improving detection whenthe compound is used in a sensor.

Having described the invention, the following examples are given toillustrate specific applications. These specific examples are notintended to limit a scope of the invention described in thisapplication.

A. Production of Hexafluorodimethylcarbinol Terminated Alkane- andAlkenethiols EXAMPLE 1

Synthesis of 4-bromo-2-butenyl-hexafluorodimethylcarbinol(BrCH₂CH═CHCH₂C(CF₃)₂(OH)-mixed geometric isomers)—This compound wasprepared by condensing 4-bromo-1-butene with hexafluoroacetone(analogous to step a of the exemplary synthesis shown above). Thereaction was conducted in a 250 mL glass lined stainless steel Parr bombfitted with a magnetic stirring bar. 4-Bromo-1-butene (4.15 g, 30.7mmol) was first weighed into the glass liner of the Parr bomb. The bombwas assembled, cooled with liquid nitrogen, and evacuated. Gaseoushexafluoroacetone (12.8 g, 77.1 mmol) was then condensed into the bomb.The sealed bomb was heated to 135° C. with stirring for a reaction timeof 72 hr. After cooling and pressure release, a dark liquid (11.04 g)crude product was obtained. Purification by distillation at reducedpressure yielded a water-white fraction (7.58 g, 82%) collected at84-86° C./8 mm Hg, which was determined to be >99% pure by gaschromatography. IR (neat/NaCl): 3600 shoulder absorption (“sh”) and 3500(free and H-bonded O—H); 3060 weak absorption (“w”) (olefinic C—H); 2960w (aliphatic C—H); 1430 (olefinic C═C), 1200 strong absorption (“s”)(C—F); 650 (C—Br). ¹H NMR (CDCl₃): 2.72 and 2.80 (doublets, 2H, forcis-trans mixture ═CH—CH₂—C(CF₃)₂(OH)); 3.00 (singlet-broad, 1H, O—H);3.92 and 3.96 (doublets for cis-trans mixture Br—CH ₂CH═); 5.77(multiplet, 1H, ═C—H); 5.92 (multiplet, 1H, ═C—H). ¹³C NMR (CDCl₃): 25.0and 27.5 (cis-trans mixture CH₂); 30.9 and 33.0 (cis-trans mixture CH₂);75.1 (—C(CF₃)20H); 123.2 (quartet CF₃); 120.8 and 124.6 (cis-transmixture C═); 131.9 and 134.0 (cis-trans mixture C═). ¹⁹F NMR (CDCl₃,Freon 113 reference) −77.02 and −77.17 (2 singlets, cis-trans mixtureCF₃). Analysis calculated for C₇H₇BrF₆O: C, 27.93; H, 2.34. Found: C,27.84; H, 2.40.

EXAMPLE 2

Synthesis of 4-mercapto-2-butenyl-hexafluorodimethylcarbinol(HSCH₂CHCHCH₂C(CF₃)₂(OH)—mixed geometric isomers)—This compound wasprepared by reacting 4-bromo-2-butenyl-hexafluorodimethylcarbinol(product of Example 1) with thiourea to form the intermediateisothiouronium salt (similar to step c of the exemplary synthesis shownabove) which was subsequently hydrolyzed by a base (NaOH) to the thiol(analogous to step d of the exemplary synthesis shown above). Thisreaction was conducted in a two-neck 25 mL round bottom flask fittedwith a magnetic stirring bar, reflux condenser and thermometer under anitrogen atmosphere. 4-Bromo-2-butenyl-hexafluorodimethylcarbinol (2.00g, 6.64 mmol) was weighed into the reaction vessel followed by ethanol(5.0 mL) and thiourea (0.52 g, 6.73 mmol). This solution was refluxed at80° C. for 3 hr. Sodium hydroxide (0.37 g, 9.2 mmol) dissolved in water(5.0 mL) was added, and the reaction mixture was refluxed at 85° C. for3 hr. The reaction was worked up by dropwise addition of the reactionmixture to 25 mL distilled water. This mixture was neutralized bydropwise addition of 1.0 M HCl until just acidic (pH paper test) thenextracted 3 times with 10 mL methylene chloride. The combined methylenechloride extracts were back extracted 2 times with 10 mL portions ofdistilled water and dried over anhydrous sodium sulfate. After filteringand rotary evaporation (50° C./20 mm Hg), 1.52 g of a yellow oil crudeproduct were obtained. This was purified by vacuum distillation to yielda fraction (1.04 g, 62%) collected at 75° C./5 mm Hg, which wasdetermined to be >99% pure by gas chromatography. IR (neat/NaCl): 3600(sh) and 3500 (free and H-bonded O—H); 3060 w (olefinic C—H); 2960 w(aliphatic C—H); 2560 w (thiol S—H); 1430 (olefinic C═C), 1200 s (C—F).¹H NMR (CDCl₃): 1.47 and 1.61 (triplets, 1H, for cis-trans mixture S—H);2.68 and 2.75 (doublets, 2H, for cis-trans mixture ═CH—CH₂-C(CF₃)₂(OH)); 3.10 (singlet-broad, 1H, O—H); 3.17 and 3.19 (tripletsfor cis-trans mixture HS—CH ₂CH═); 5.55 (multiplet, 1H, ═C—H); 5.82(multiplet, 1H, ═C—H). ¹³C NMR (CDCl₃): 20.3 and 26.2 (cis-trans mixtureCH₂); 28.0 and 33.1 (cis-trans mixture CH₂); 75.1 (—C(CF₃)₂OH); 123.0(quartet, CF₃); 120.0 and 121.0 (cis-trans mixture C═); 135.3 and 137.7(cis-trans mixture C═). ¹⁹F NMR (CDCl₃, Freon 113 reference) −76.84 and−77.05 (2 singlets, cis-trans mixture CF₃). Analysis calculated forC₇H₈F₆OS: C, 33.08; H, 3.17. Found: C, 32.98; H, 3.27.

EXAMPLE 3

Synthesis of 5-bromo-3-pentenyl-hexafluorodimethylcarbinol(BrCH₂CH₂CH═CHCH₂C(CF₃)₂(OH)—mixed geometric isomers) (structure 2)—Thiscompound was prepared by condensing 5-bromo-1-pentene (structure 1) withhexafluoroacetone (step a of the exemplary synthesis shown above). Thereaction was conducted in a 250 mL glass lined stainless steel bombfitted with a magnetic stirring bar. 5-Bromo-1-pentene (4.36 g, 29.3mmol) was weighed into the glass liner of the Parr bomb. The bomb wasassembled, cooled with liquid nitrogen, and evacuated. Gaseoushexafluoroacetone (13.6 g, 81.9 mmol) was then condensed into the bomb.The sealed bomb was heated to 140° C. with stirring for a reaction timeof 72 hr. After cooling and pressure release, a dark liquid (9.20 g)crude product was obtained. Purification by distillation at reducedpressure yielded a water-white fraction (8.50 g, 92%) collected at 65°C./1 mm Hg, which was determined to be >99% pure by gas chromatography.IR (neat/NaCl): 3600 (sh) and 3500 (free and H-bonded O—H); 3060 w(olefinic C—H); 2960 w (aliphatic C—H); 1430 (olefinic C═C), 1200 s(C—F); 650 (C—Br). ¹H NMR (CDCl₃): 2.65 (broad multiplet, 4H, —CH—CH₂—); 3.10 (singlet-broad, 1H, O—H); 3.43 (triplet, 2H, Br—CH ₂—); 5.55(multiplet, 1H, ═C—H); 5.7 (multiplet, 1H, ═C—H). ¹³C NMR (CDCl₃): 28.2and 30.5 (cis-trans mixture CH₂); 32.4 and 33.5 (cis-trans mixture CH₂);35.2 CH₂; 74.8 (—C(CF₃)₂OH); 123.1 (quartet CF₃); 121.3 and 123.2(cis-trans mixture C═); 134.5 and 136.8 (cis-trans mixture C═). ¹⁹F NMR(CDCl₃, Freon 113 reference) −77.13 and −77.33 (2 singlets, cis-transmixture CF₃). Analysis calculated for C₈H₉BrF₆O: C, 30.50; H, 2.88.Found: C, 30.44; H, 2.95.

EXAMPLE 4

Synthesis of 5-mercapto-3-pentenyl-hexafluorodimethylcarbinol(HSCH₂CH₂CH═CHCH₂C(CF₃)₂(OH)—mixed geometric isomers) (structure 4)—Thiscompound was prepared by reacting5-bromo-1-pentenyl-hexafluorodimethylcarbinol (structure 2, product ofExample 3) with thiourea to form the intermediate isothiouronium salt,which was subsequently hydrolyzed by a base to the thiol as for Example2. This reaction was conducted in a two-neck 25 mL round bottom flaskfitted with a magnetic stirring bar, reflux condenser and thermometerunder a nitrogen atmosphere.5-Bromo-2-pentenyl-hexafluorodimethylcarbinol (2.50 g, 7.93 mmol) wereweighed into the reaction vessel followed by ethanol (5.0 mL) andthiourea (0.612 g, 8.04 mmol). This solution was refluxed at 84° C. for2.5 hr. Sodium hydroxide (0.44 g, 11.0 mmol) dissolved in water (5.0 mL)was added, and the reaction mixture was refluxed at 87° C. for 2.5 hr.The reaction was worked up by dropwise addition of the reaction mixtureto 25 mL distilled water. This mixture was neutralized by dropwiseaddition of 1.0 M HCl until just acidic (pH paper test) then extracted 3times with 20 mL methylene chloride. The combined methylene chlorideextracts were back extracted 2 times with 10 mL portions distilled waterand dried over anhydrous sodium sulfate. After filtering and rotaryevaporation (50° C./20 mm Hg), 1.84 g a yellow oil crude product wereobtained. This was purified by vacuum distillation to yield a fraction(1.32 g, 65%) collected at 65° C./1 mm Hg, which was determined tobe >99% pure by gas chromatography. IR (neat/NaCl): 3600 (sh) and 3470(free and H-bonded O—H); 3050 w (olefinic C—H); 2940 w (aliphatic C—H);2550 w (thiol S—H); 1430 (olefinic C═C), 1200 s (C—F). ¹H NMR (CDCl₃):1.30 and 1.42 (triplets, 1H, for cis-trans mixture S—H); 2.38(multiplet, 2H, CH ₂SH); 2.61 (multiplet, 2H, for cis-trans mixture═CH—CH ₂); 2.70 and 2.75 (doublets, 2H, for cis-trans mixture ═CH—CH₂—C(CF₃)₂(OH); 3.33 (singlet-broad, 1H, O—H); 5.49 (multiplet, 1H,═C—H); 5.65 (multiplet, 1H, ═C—H). ¹³C NMR (CDCl₃): 23.9 and 27.3(cis-trans mixture CH₂); 30.1 and 33.4 (cis-trans mixture CH₂); 36.1CH₂; 123.1 (quartet CF₃); 121.2 and 123.0 (cis-trans mixture C═); 136.2and 138.0 (cis-trans mixture C═). ¹⁹F NMR (CDCl₃, Freon 113 reference)−77.11 and −77.33 (2 singlets, cis-trans mixture CF₃). Analysiscalculated for C₈H₁₀F₆OS: C, 35.82; H, 3.76. Found: C, 35.79; H, 3.79.

EXAMPLE 5

Synthesis of 5-bromopentyl-hexafluorodimethylcarbinol(BrCH₂CH₂CH₂CH₂CH₂C(CF₃)₂(OH)) (structure 3)—This compound was preparedby hydrogenating (step b of the exemplary synthesis shown above)5-bromo-3-pentenyl-hexafluorodimethylcarbinol (structure 2, product ofExample 3) over a 10% palladium/carbon catalyst. The reaction wasconducted in a 250 mL glass lined stainless steel bomb fitted with amagnetic stirring bar. The 10% palladium/carbon catalyst (0.25 g),ethanol (25 mL) and 4-bromo-2-butenyl-hexafluorodimethylcarbinol (2.00g, 6.35 mmol) were weighed into the glass liner of the Parr bomb. Thebomb was assembled, cooled with liquid nitrogen, evacuated, charged withhydrogen, pumped out, and recharged with hydrogen at an initial pressureof 1050 psi. This reaction was stirred at 22° C. for 72 hr during whichthe pressure dropped to 1010 psi. After pressure release, the bomb wasopened and the liquid mixture filtered through Celite to remove theparticulate carbon and yield a clear yellow solution which was reducedto 3.20 g of a yellow oil after evaporation of the ethanol. Vacuumdistillation of the oil yielded two fractions, one of 1.35 g collectedat 50-55° C./5 mm and the second of 0.60 g collected at 80-90° C./5 mm.The second fraction (28% yield) was 95% pure by gas chromatography andanalyzed as the product. IR (neat/NaCl): 3600 (sh) and 3500 (free andH-bonded O—H); 2950 m and 2900 w (aliphatic C—H); 1200 s (C—F). ¹H NMR(CDCl₃): 1.48 (broad multiplet, 4H, —CH ₂—); 1.88 (multiplet, 4H, —CH₂—); 2.84 (broad singlet, 1H, O—H); 3.49 (triplet, 2H, BrCH ₂—). ¹³C NMR(CDCl₃): 20.9, 28.5, 30.7, 32.4 and 34.0 (CH₂); 76.5 (—C(CF₃)₂OH); 123.1(quartet CF₃). ¹⁹F NMR (CDCl₃, Freon 113 reference) −77.10 (singlet,CF₃). Analysis calculated for C₈H₁₁BrF₅O: C, 30.30; H, 3.50. Found: C,30.19; H, 3.61.

EXAMPLE 6

Synthesis of 5-mercaptopentyl-hexafluorodimethylcarbinol(HSCH₂CH₂CH₂CH₂CH₂C(CF₃)₂(OH)—mixed geometric isomers) (structure5)—This compound was prepared by reacting5-bromopentyl-hexafluorodimethylcarbinol (structure 3, product ofExample 5) with thiourea to form the intermediate isothiouronium salt,which was subsequently hydrolyzed by a base to the thiol as for Example2. This reaction was conducted in a two-neck 25 mL round bottom flaskfitted with a magnetic stirring bar, reflux condenser and thermometerunder a nitrogen atmosphere. 5-Bromopentyl-hexafluorodimethylcarbinol(0.60 g, 1.89 mmol) was weighed into the reaction vessel followed byethanol (5.0 mL) and thiourea (0.146 g, 1.92 mmol). This solution wasrefluxed at 81° C. for 3 hr. Sodium hydroxide (0.10 g, 2.62 mmol)dissolved in water (3.0 mL) was added, and the reaction mixture wasrefluxed at 84° C. for 3 hr. The reaction was worked up by dropwiseaddition of the reaction mixture to 10 mL distilled water. This mixturewas neutralized by dropwise addition of 1.0 M HCl until just acidic (pHpaper test) then extracted 3 times with 10 mL methylene chloride. Thecombined methylene chloride extracts were back extracted 2 times with 5mL portions distilled water and dried over anhydrous sodium sulfate.After filtering and rotary evaporation (50° C./20 mm Hg), 0.43 g ayellow oil crude product was obtained. This was purified by vacuumdistillation to yield a fraction (0.26 g, 51%) collected at (80-90° C./1mm Hg) determined to be >90% pure by gas chromatography. IR (neat/NaCl):3600 (sh) and 3470 (free and H-bonded O—H); 2950 w (aliphatic C—H); 2560w (thiol S—H); 1200 s (C—F). ¹H NMR (CDCl₃): 1.40 (triplet, 1H, S—H);1.45 (broad multiplet, 4H, —CH ₂—); 1.68 (multiplet, 2H, CH ₂); 1.88(multiplet, 2H, CH ₂); 2.34 (multiplet, 2H, CH ₂SH); 3.23(singlet-broad, 1H, O—H); ¹³C NMR (CDCl₃): 20.6, 25.6, 28.1, 30.4 and33.2 (CH₂); 77.8 (—C(CF₃)₂OH); 123.2 (quartet CF₃). ¹⁹F NMR (CDCl₃,Freon 113 reference) −77.05 (singlet, CF₃). Analysis calculated forC₈H₁₂F₆OS: C, 35.56; H, 4.48. Found: C, 35.48; H, 4.55.

B. Preparation of Gold Nanoclusters using Fluoroalcohol Ligands of theExemplary Compounds

EXAMPLE 7

Direct synthesis method for gold nanocluster stabilized by4-mercapto-2-butenyl-hexafluorodimethylcarbinol(HSCH₂CH═CHCH₂C(CF₃)₂(OH))—Solutions of: 1.52 g tetraoctylammoniumbromide ((C₈H₁₇)₄NBr) in 56 mL toluene; 0.2865 (0.727 mmol) hydrogentetrachloroaurate (III) trihydrate (HAuCl₄·3H₂O) in 21 mL distilledwater (analogous to step S110 above); 0.1847 g (0.727 mmol)4-mercapto-2-butenyl-hexafluorodimethylcarbinol(HSCH₂CH═CHCH₂C(CF₃)₂(OH)) in 2 mL toluene; and 0.2800 g (7.4 mmol)sodium borohydride (NaBH₄) (analogous to step S120 above) in 17.5 mLdistilled water are prepared. With rapid stirring the HAuCl₄/watersolution is slowly added to the (C₈H₁₇)₄NBr/toluene solution. After 2minutes, the HSCH₂CH═CHCH₂C(CF₃)₂(OH)/toluene solution is added followedby the slow addition of the NaBH₄/water solution with very rapidstirring. The vigorous stirring is continued for 3 hr. The toluene phaseis then separated and concentrated (5° C./25 mm rotary evaporation) to a5 mL volume. This concentrated reaction mixture is added dropwise to 100mL stirred diethyl ether, and the precipitated product collected bycentrifugation as a thick oily crude product. After washing three timeswith 10 mL portions of diethyl ether, the crude product is purified bycolumn chromatography. The product is dissolved in 2 mL CHCl₃, loadedonto a chromatographic column of silica packed in CHCl₃ and eluted withethyl acetate to yield 0.31 g product. Subsequent elution with CH₃OHyields 0.15 g of cluster contaminated with (C₈H₁₇)₄NBr. The IR spectrumof the purified product is identical to that of theHSCH₂CH═CHCH₂C(CF₃)₂(OH) free thiol with the exception of thedisappearance of the 2560 cm⁻¹ S—H stretch.

EXAMPLE 8

Direct synthesis method for gold nanocluster stabilized by5-mercapto-3-pentenyl-hexafluorodimethylcarbinol(HSCH₂CH₂CH═CHCH₂C(CF₃)₂(OH)) (structure 4)—Solutions of: 1.52 gtetraoctylammonium bromide ((C₈H₁₇)₄NBr) in 56 mL toluene; 0.2851 (0.724mmol) hydrogen tetrachloroaurate (III) trihydrate (HAuCl₄·3H₂O) in 21 mLdistilled water (analysis similar to step S110 above); 0.1917 g (0.715mmol) 5-mercapto-3-pentenyl-hexafluorodimethylcarbinol(HSCH₂CH₂CH═CHCH₂C(CF₃)₂(OH)) in 2 mL toluene; and 0.2785 g (7.37 mmol)sodium borohydride (NaBH₄) (analogous to step S120 above) in 17.5 mLdistilled water are prepared. With rapid stirring the HAuCl₄/watersolution is slowly added to the (C₈H₁₇)₄NBr/toluene solution. After 2minutes, the SCH₂CH₂CH═CHCH₂C(CF₃)₂(OH)/toluene solution is addedfollowed by the slow addition of the NaBH₄/water solution with veryrapid stirring. The vigorous stirring is continued for 3 hr. The toluenephase is then separated and concentrated (50° C./50 mm rotaryevaporation) to a 5 mL volume. This concentrated reaction mixture isadded dropwise to 100 mL stirred diethyl ether, and the precipitatedproduct collected by centrifugation as a thick oily crude product. Afterwashing three times with 10 mL portions of diethyl ether, the crudeproduct is purified by column chromatography. The product is dissolvedin 2 mL CHCl₃, loaded onto a chromatographic column of silica packed inCHCl₃ and eluted with ethyl acetate to yield 0.20 g product. Subsequentelution with CH₃OH yields 0.23 g of cluster contaminated with(C₈H₁₇)₄NBr. The IR spectrum of the purified product is identical tothat of the HSCH₂CH₂CH═CHCH₂C(CF₃)₂(OH) free thiol with the exception ofthe disappearance of the 2560 cm⁻¹ S—H stretch.

EXAMPLE 9

Ligand exchange method for synthesis of gold nanocluster stabilized by4-mercapto-2-butenyl-hexafluorodimethylcarbinol(HSCH₂CH═CHCH₂C(CF₃)₂(OH))—Three successive exchange steps wereconducted. To a 50 mL pear shaped flask fitted with a stirring bar andtight fitting cap were added 1.11 g Au:C8(1:1) (a gold nanoclusterformed from HAuCl₄ and octanethiol (analogous to step S150 above), seeU.S. Pat. No. 6,221,673), 2.0 mL CHCl₃ and 0.7767 gHSCH₂CH═CHCH₂C(CF₃)₂(OH). The reaction mixture was stirred for 24 hoursthen concentrated to dryness by rotary evaporation followed by vacuumdrying (1 mm/23° C.) and a 15 mL pentane rinse/decant to remove freethiol. For the second step, 0.7716 g HSCH₂CH═CHCH₂C(CF₃)₂(OH) and 20 mLCH₃OH were added to the exchange product in the reaction flask(analogous to step S150 above). The solution was again stirred for 24 hrthen concentrated to dryness by rotary evaporation followed by vacuumdrying (1 mm/23° C.) and a 15 mL pentane rinse/decant to remove freethiol. For the third step, 0.7777 g HSCH₂CH═CHCH₂C(CF₃)₂(OH) and 20 mLCH₃OH were added to the reaction flask (analogous to step S170 above).This solution was again stirred for 24 hr followed by concentration todryness by rotary evaporation, vacuum drying (1 mm/23° C.), and a 15 mLpentane rinse/decant to remove free thiol. The product was thenextracted 12 hr with pentane and vacuum dried to yield 0.8122 g. The IRspectrum was identical to that of the HSCH₂CH═CHCH₂C(CF₃)₂(OH) freethiol with the exception of the disappearance of the 2560 cm⁻¹ S—Hstretch.

EXAMPLE 10

Ligand exchange method for synthesis of gold nanocluster stabilized by5-mercapto-3-pentenyl-hexafluorodimethylcarbinol(HSCH₂CH₂CHCHCH₂C(CF₃)₂(OH)) (structure 4)—Three successive exchangesteps were conducted. To a 50 mL pear shaped flask fitted with astirring bar and tight fitting cap were added 0.1500 g Au:C8(1:1) (asdescribed above), 2.0 mL CHCl₃ and 0.1706 g HSCH₂CH₂CH═CHCH₂C(CF₃)₂(OH).The reaction mixture was stirred for 24 hours then concentrated todryness by rotary evaporation followed by vacuum drying (1 mm/23° C.)and a 2 mL pentane rinse/decant to remove free thiol. For the secondstep, 0.1026 g HSCH₂CH═CHCH₂C(CF₃)₂(OH) and 1.5 mL 2-propanol were addedto the exchange product in the reaction flask (analogous to step S150above). The solution was again stirred for 24 hr then concentrated todryness by rotary evaporation followed by vacuum drying (1 mm/23° C.)and a 2 mL pentane rinse/decant to remove free thiol. For the thirdstep, 0.0998 g HSCH₂CH═CHCH₂C(CF₃)₂(OH) and 1.5 mL CH₃OH were added tothe reaction flask (analogous to step S170 above). This solution wasagain stirred for 24 hr followed by concentration to dryness by rotaryevaporation, vacuum drying (1 mm/23° C.) and three cycles of 2 mLpentane rinse/decant to remove free thiol. The product was thenextracted 12 hr with pentane and vacuum dried to yield 0.2513 g. The IRspectrum was identical to that of the HSCH₂CH═CHCH₂C(CF₃)₂(OH) freethiol with the exception of the disappearance of the 2560 cm⁻¹ S—Hstretch.

EXAMPLE 11

Ligand exchange method for synthesis of gold nanocluster stabilized by amixture 4-mercapto-2-butenyl-hexafluorodimethylcarbinol(HSCH₂CH═CHCH₂C(CF₃)₂(OH)) and hexanethiol (HS(CH₂)₅CH₃)—One exchangestep was conducted. To a 10 mL pear-shaped flask fitted with a tightfitting cap were added 0.1012 g Au:C6(1:1) (a gold nanocluster formedfrom HAuCl₄ and hexanethiol, see U.S. Pat. No. 6,221,673), 2.0 mL CHCl₃,and 0.0193 g HSCH₂CH═CHCH₂C(CF₃)₂(OH). The reaction mixture was stirredfor 24 hours then concentrated to dryness by rotary evaporation followedby vacuum drying (1 mm/2° C.). The product was rinsed two times with 2mL quantities of pentane in which it has a slight solubility and vacuumdried (1 mm/23° C.) to yield 0.0870 g. The quantities of product in thefirst and second pentane washes were 0.0059 g and 0.0023 g respectively.IR spectra displayed bands characteristic of both theHSCH₂CH═CHCH₂C(CF₃)₂(OH) and the HS(CH₂)₅CH₃ ligands, and, from the C—Fstretching (1200 cm⁻¹) and C—H stretching of the CH₃ group, a relativeligand composition of 2:3 HSCH₂CH═CHCH₂C(CF₃)₂(OH): HS(CH₂)₅CH₃ wasdetermined for the shell.

EXAMPLE 12

Ligand exchange method for synthesis of gold nanocluster stabilized by amixture 5-mercapto-3-pentenyl-hexafluorodimethylcarbinol(HSCH₂CH₂CH═CHCH₂C(CF₃)₂(OH)) (structure 4) and hexanethiol(HS(CH₂)₅CH₃)—One exchange step was conducted. To a 10 mL pear-shapedflask fitted with a tight fitting cap were added 0.1022 g Au:C6(1:1) (asabove), 2.0 mL CHCl₃, and 0.0203 g HSCH₂CH═CHCH₂C(CF₃)₂(OH). Thereaction mixture was stirred for 24 hours then concentrated to drynessby rotary evaporation followed by vacuum drying (1 mm/23° C.). Theproduct was rinsed two times with 2 mL quantities of pentane in which ithas a slight solubility and vacuum dried (1 mm/23° C.) to yield 0.0888g. The quantities of product in the first and second pentane washes were0.0045 g and 0.0035 g respectively. IR spectra displayed bandscharacteristic of both the HSCH₂CH₂CH═CHCH₂C(CF₃)₂(OH) and theHS(CH₂)₅CH₃ ligands, and, from the C—F stretching (1200 cm⁻¹) and C—Hstretching of the CH₃ group, a relative ligand composition of 2:3HSCH₂CH═CHCH₂C(CF₃)₂(OH): HS(CH₂)₅CH₃ was determined for the shell.

The exemplary embodiment has been described with reference to thepreferred embodiments. Obviously, modifications and alterations willoccur to others upon reading and understanding the preceding detaileddescription. It is intended that the exemplary embodiment be construedas including all such modifications and alterations insofar as they comewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A method of making a hexafluorodimethylcarbinolterminated thiol compound, comprising: reacting a ω-halo-α-olefin withhexafluoroacetone to form a first intermediate comprising an alkenylgroup; optionally hydrogenating the first intermediate to form a secondintermediate comprising an alkyl group; reacting at least one of thefirst and second intermediates with thiourea to form a thiouroniumhalide adduct; and decomposing the thiouronium halide adduct followed byhydrolysis with a base to form the compound.
 2. The method of claim 1;wherein the ω-halo-α-olefin includes the formula CH₂═CH—CH₂-M-X; whereinM is selected from a substituted or unsubstituted methylene chain, asubstituted or unsubstituted oxyalkylene chain, and an alkyl-substitutedor unsubstituted silicon-containing chain, and combinations andmultiples thereof; and wherein X represents a halogen.
 3. The method ofclaim 2; wherein M is selected from —(CH₂)_(n)—, —(OCH₂CH₂)_(m)—, and—(Si(CH₃)₂O)_(p)—Si(CH₃)₂—(CH₂)_(q)—; and wherein n>0; m>0; p≧0; andq≧1.
 4. The method of claim 1; wherein M is —(CH₂)_(n)—; and wherein nis 1 or 2.